Previously, expandable chucks and core-shafts were operated mechanically or by a single fluid system, either gas or liquid, which single fluid system usually inflated an expandable elastic bag inside the shaft to radially extend plungers, leaves or bars around the shaft as shown in Ochs et al. U.S. Pat. No. 3,908,926 issued Sept. 30, 1975. The limit of the pressure which could be applied per square inch to these bags without causing their rupture was usually about 200 psi, which automatically limited the grip that any of such chucks or expandable core-shafts could exert. Furthermore, these single fluid hydraulic systems were usually operated and controlled from a pressure source outside the chuck or shaft, thereby requiring a continuous connection between the source and the shaft, which also gave rise to leakage problems under high pressures because of the relative movement at the joint between the outside stationary duct and the rotating duct of the shaft. However, a self-contained pressurized fluid supply device is also known for a chuck in the Atherholt Jr. U.S. Pat. No. 3,122,376 issued Feb. 25, 1964.
Still further, self-contained prior art systems usually had difficulty in maintaining internal pressures, particularly if pressures were above about 200 psi, because of sealing problems between the movable parts, namely the edges of the pistons that operated the radial extending plungers or in the limit of the strength of the bag or expandable flexible chamber used in operating the plungers.